Portable, hand-held power cutters powered by a single cylinder internal combustion engine are known since long. As well known in the art, a muffler is provided at the exhaust port of the engine for collecting the exhaust gases. Because of size and weight constraints such a hand held tool has small or even minimized cooling fins on the engine cylinder as well as a small/minimized cooling fan. Therefore the temperature in the cylinder is often near/at critical levels during hard use and the exhaust port area on the hot, front side of the cylinder is the most critical for heat damage to cylinder and piston. This temperature problem is even more marked if a catalyser is arranged in the muffler, that therefore will be even more hot and transfer heat to the exhaust port area. Other features like a delayed ignition, e.g. to prevent over revving in combination with ignition “cut out”, will also create more heat in the muffler and in the exhaust port area of the cylinder, and especially if a post oxidation, or “after burn” is started in the muffler. This risk is also higher in a two stroke engine provided with additional air. Power cutters are especially problematic as their “cut out” speed is very close to their normal work speed, like only 2-15% above. An exhaust gas inlet is provided on the muffler to communicate with the exhaust port of the engine cylinder and finally the exhaust gases are released in the atmosphere via the outlet of the muffler. Primarily, the muffler is placed in close vicinity of the engine cylinder due to the space and size constraints in the handheld power cutter. During and after operation, a lot of heat is transferred from the inlet port of the muffler to the exhaust port and may increase the temperature at the exhaust port of the cylinder. The increase in temperature may result in engine damage and failure. These machines are often used for cutting concrete and similar materials. Such a cutting creates a lot of abrasive particulate matter. Typically, efficient air cleaning is vital and is attained mainly through a filter assembly having a big filter volume, which may increase the service life of the machine. To create a big filter volume in a compact machine, power cutters have been introduced which have an engine cylinder which is leaned forwards. An example is Husqvarna K 750 and K760. This design is described in U.S. Pat. No. 7,520,276, assigned to Husqvarna AB and the disclosure of which is hereby incorporated by reference in this application.
This kind of design layout has a forward leaning cylinder with a tilt angle (α) that is between 5 degrees and 40 degrees in contrast to a more traditional design with a backwards leaning cylinder, i.e. with a negative tilt angle. Further the cutter arm points more upwards than in a traditional design. These differences contributes in creating an acute angle between the cutter arm centerline and the cylinder bore centerline, and this acute angle is larger than 45° but smaller than 75°. It is typically 55°-60°, compared to 80°-100° for a more traditional design. So this design enables a compact and light power cutter with a very good air cleaning. However, when built in this compact design with the muffler partly below the cylinder, the engine tends to be somewhat hotter than in a more traditional design.
U.S. Pat. No. 7,389,853 issued on Jun. 24, 2008 and assigned to Briggs & Stratton Corporation, describe a muffler disposed above the cylinder of the engine. As described in the U.S. Pat. No. 7,389,853, the muffler is provided with a pipe which attaches the inlet of the muffler to the exhaust port of the engine cylinder. Further, U.S. Pat. No. 6,250,422 issued on Jun. 26, 2001 and assigned to Nelson Industries, also discloses a similar muffler construction and a similar engine-muffler configuration, where the muffler is intended to be disposed above the engine. If using a layout with a muffler disposed above the cylinder it is extremely difficult to achieve a compact configuration for the handheld power cutter, and the result would also be a high cutter with a high center of gravity, which would be very negative for a hand held power cutter.
Therefore there is a need for a muffler construction and engine-muffler arrangement to protect the engine from damages due to overheating and also provided a compact configuration of the handheld power cutter.